Genera

Family STERNOPTYCHIDAE

Silhouette

Family of small, silvery bioluminescent fishes living the deep oceanic midwaters. Many species have extremely compressed bodies with a deep keel, large eyes, upturned mouths and groups of photophores along the ventral surface and lower sides of the head and body.

Marine hatchetfishes are very well-camouflaged for life in the oceanic 'twilight' zone. The combination of very silvery sides, downwardly-directed photophores and a darkly-pigmented dorsal surface disrupts their body silhouette, hiding them from predators and prey.

Many species undertake daily vertical migrations to feed at night in shallower waters where food is more plentiful.

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Family Taxonomy

Family with 10 genera and about 75 species in two subfamiles. Twenty-two described species in 6 genera are known from Australian waters.

Family Distribution

Found worldwide in temperate and tropical parts of all oceans. Although most species are mesopelagic, some are bathy- or benthopelagic. Species are found at depths of 100-1260 m, usually below 400 m during the day.

Many sternoptychids undertake diurnal vertical migrations to feed at night in shallower waters where food is more plentiful, returning to deeper waters during the day.

Family Description

Body moderately elongate to very compressed and deep; prominent photophores ventrolaterally on head and body, some series united into distinct clusters of two or more photophores.

Mesopelagic planktivores feeding on small planktonic crustaceans such as copepods, amphipods and eupahisids.

Family Reproduction

Marine hatchetfishes are oviparous (egg-layers) with planktonic eggs and larvae.

Eggs and larvae of the Subfamily Sternoptychinae are poorly known as they are usually found below 200 m where there has been little collecting with plankton nets.

Larvae of several species of the Subfamily Maurolicinae are usually found in shallower waters and are well-known. Eggs small, buoyant, 0.5-1.65 mm diameter. Larvae long, slender at hatching, some become very deep-bodied with long tails, others remaining slender. Larval identification is based on photophore patterns, fin position and fin-ray counts; photophores develop gradually, some coalesce into gland-like structures.

Family Remarks

Hatchetfishes are very well-camouflaged for life in deep waters of the open ocean. The combination of very silvery sides, downwardly-directed photophores and a darkly-pigmented dorsal surface disrupts their body silhouette, hiding them from predators.

The light emitted from the photophores is thought to match that filtering down from above, so that predators looking upwards cannot see the body outline.

Some species have evolved tubular eyes with large lenses which improve the vision by concentrating the dim light of the deep-sea.